1. Field of the Invention
The present invention relates to a phase shift amount measurement apparatus for measuring a phase shift amount of a phase shift mask.
Further, the present invention relates to a transmittance measurement apparatus for measuring the transmittance of a light shielding pattern of a photo-mask.
2. Description of the Related Art
As photo-masks designed to handle the miniaturization of LSIs, half-tone type phase shift masks and Levenson type phase shift masks have been put into practical use. The phase shift masks are designed so as to give a phase difference of π or an odd number of times of that to light passing through adjacent pattern elements of a mask pattern. The resolution of the exposed pattern falls along with the deviation from the design value and the quality as a photo-mask is lowered. For this reason, in the production process of a photo-mask, the phase shift amount is an important parameter for securing the quality. The phase shift amount of a phase shift mask is measured by using a phase shift amount measurement apparatus.
In a conventional phase shift amount measurement apparatus, the measurement was carried out by forming a test pattern on a corner portion of a quartz substrate of the photo-mask, measuring the phase shift amount of the test pattern, and estimating the phase shift amount of an actually used mask pattern (real pattern) based on the measurement result. However, along with the miniaturization of photo-masks, the demand for not measurement according to the test pattern, but the measurement of the phase shift amount of the mask pattern used in actual exposure has becomes stronger. Development of a phase shift amount measurement apparatus able to correctly measure the phase shift amount of an actual pattern has been demanded.
As an apparatus for measuring the phase shift amount of a half tone type phase shift mask, an apparatus projecting illumination light toward the phase shift mask to be checked, making the light transmitted from an opening portion of the phase shift mask and light transmitted from a phase shifter to interfere with each other by using a two-beam interferometer, receiving the emitted interference light by a photomultiplier, and measuring the phase shift amount based on an output signal from the photomultiplier is known (see for example Japanese Patent Publication (A) No. 11-327119).
In a case of measuring the phase shift amount of the actual mask of the half-tone type phase shift mask and a Levenson type phase shift mask, there is the inconvenience that when a pattern edge portion of the mask approaches the light measurement region, strong diffraction light generated by the pattern edge portion enters the light measurement region and becomes noise light. In particular, in a conventional phase shift amount measurement apparatus, interference light emitted from an interference optical system is received by the photomultiplier. Therefore, not only the measurement light, but also the multi-reflected light in the optical system and stray light due to aberration of the lenses strike the photomultiplier, so there was a limit to the measurement precision and reliability. Namely, when measuring interference light by using a single light receiving element having a relatively large light receiving area like a photomultiplier, the diffraction light from the pattern edge portion etc., the multi-reflected light, and so on strike the photomultiplier together with the normal measurement light. The light amount value including the amounts of these lights is output from the photomultiplier. Further, the phase amounts and luminances of these undesired external lights greatly differ from the phase amount etc. of the normal measurement light. Accordingly, when measuring the phase shift amount by using the output signal from a photomultiplier, a large error occurs in the measured phase shift amount.
Further, along with the miniaturization of LSIs, there is a strong demand for managing the transmittance of the light shielding pattern forming the actual mask and for development of a transmittance measurement apparatus able to measure the transmittance of the light shielding pattern of an actual mask with a wide dynamic range.